Physique
Propagation caracteristics of chirped vector soliton in birefringent optical fibers with variable coefficients in the presence of third order dispersion
We study in this work, the propagation characteristics of chirped vector solitons in optical fiber systems using the compact split step Padé scheme (CSSPS). This study is done in the case of variable coefficients and the presence of third order dispersion. A negative chirp makes the soliton broadening, while; a positive chirp leads to a soliton compression. The effect of chirp on the soliton temporal width of an amplification system (σ>0) is greater than that in a loss system (σ<0). In the presence of third order dispersion, we note an increase of the pulse width with an asymmetric oscillation on the trailing edge. In the same time, we note a shift of the center of the two components of the one managed chirped vector soliton along the propagation distance. Voir les détails
Mots clés : vector soliton, chirped soliton, optical fibers, compact split step Padé scheme, coupled higher-order nonlinear Schrodinger equations, dispersion management, nonlinearity management, temporal waveform, third order dispersion.
Structural modification and magnetic properties enhancement with Er3+, of sol-gel TiO2 thin films
Nano-crystalline un-doped and erbium doped TiO2 thin films were dip-coated on glass substrates by sol-gel method. The films were annealed at 450 °C during 1 hour. DSC results show that the crystallization effectuates at 339°C for un-doped TiO2, whereas for erbium doped TiO2 the crystallization occurs earlier with two separated exothermic. XRD diagrams illustrate that un-doped and erbium doped TiO2 crystallize in anatase phase only and indicate that the crystallite size decreases from 24 to 21 nm as a function of the increase in Er3+ content. This result is confirmed by Raman spectra. Moreover, the VSM results indicate, on one hand, a ferromagnetic behaviour of the un-doped TiO2. On the other hand, the incorporation of Erbium leads to an enhancement of the ferromagnetic behaviour. It is worthy to mention that the weak Er3+ doping (0.1 at.%) is the high ordered magnetically with highest saturation magnetization of 1.92 memu. Both elaborated TiO2 and Er:TiO2 films show good structural properties and have a diluted magnetic semiconductors structure. The films are promising for the possible applications in optoelectronic devices. Voir les détails
Mots clés : TiO2 doped Er3+, Structural properties, sol-gel, Magnetic Properties, oxygen vacancies.
PROPRIETES ELECTRONIQUES DES NANOCOMPOSITES Ni/MgO
Le but de ce travail est d'étudier les propriétés électronques des nanocomposites Ni/MgO, obtenus par imprégnation avec échange ionique, suivie soit d’une irradition gamma, soit d’une calcination diverses températures (T=100-600°C). La diffraction des rayons X a révélé la formation de l’hydroxyde de magnésium après l’étape d’imprégnation. Après traitement thermique, cette phase disparait au détriment de composés intermétalliques Mg-Ni (Mg2Ni, Mg6Ni et Ni2Mg), qui à leurs tour disparraissaient audela de 300°C.L’étude ds propriétés électroniques des composites Ni/MgO par la spectroscopie (XPS), a confirmer la formation de composés intermétalliques Ni-Mg, et qui affecte l’energie de liaison de l’oxyde de nickel (NiO) détécté en surface. Voir les détails
Mots clés : Ni-MgO, nanoparticules, XPS
Etude des proprietés structurales , élastiques et électronique de CuS et CuTe par la méthode FP-LMTO
The aim of this work is to study the structural ,electronic and elastic properties of CuS. for this, we use the full-potential linear muffin-tin orbital (FP-LMTO) method in the framework of density-functional theory (DFT). The exchange and correlation energy is described in the generalized gradient approximation (GGA ) using Perdew-Wang parameterization. We have investigated the effect of composition on structural properties such as lattice constants, bulk modulus and band gap. We report the results concerning the variation of thegaps and crossover of the direct, indirect band gap and bowing .Finally, a reasonable agreement is found from the comparison of our results with other theoretical calculations. Voir les détails
Mots clés : CuS, FP-LMTO, electronic properties, elastic proprieties
Structural, Mechanical, Electronic, Elastic and Chemical Bonding Properties of the Complex K2PtCl6-Structure Hydrides Sr2RuH6 First-Principles Study
We report a systematic study of the structural, electronic and elastic properties of the ternary ruthenium-based hydrides Sr2RuH6 within two complementary first-principles approaches. We describe the properties of the Sr2RuH6 systems looking for trends on different properties. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gap is about 2.99eV. Calculated density of states spectra demonstrate that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time. Voir les détails
Mots clés : Ruthenium-based hydrides; first-principles calculations; elastic constants; electronic structure
Simulation du L’implantation ionique du phosphore dans la matrice de ZnO
Le matériau ZnO montre de manière quasi-naturelle un dopage de type n [1]. Son dopage de type p représente une importante problématique récurrente depuis plus d'une quinzaine d'années. Dans ce travail nous avons fait une simulation numérique du dopage de ZnO en type p. Pour cela, nous avons utilisé le code dénommée TRIM (Transport and Range of Ions in Matter) et SRIM (Stopping and range of Ions in Matter) développé par Ziegler et al [2].C’est une simulation faite pour caractériser l'interaction des ions avec des cibles échantillons en gaz ou en solides. Les résultats numériques visent à étudier l'interaction d'un faisceau d'ions avec la surface semi-conductrice du ZnO. Dans notre étude le bombardement des ions du phosphore P tombe sur la cible ZnO selon une incidence normale au plan de la surface du matériau avec la possibilité de former des postes vacants sur la zone irradiée le composé de type II-VI ZnO Voir les détails
Mots clés : ZnO, SRIM, TRIM
Structural, electronic, optical and elastic properties of the complex K2PtCl6-structure hydrides ARuH6 (A = Mg, Ca, Sr and Ba): first-principles study
We report a systematic study of the structural, electronic, optical and elastic properties of the ternary ruthenium-based hydrides A2RuH6 (A = Mg, Ca, Sr and Ba) within two complementary first-principles approaches. We describe the properties of the A2RuH6 systems looking for trends on different properties as a function of the A sublattice. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gaps are about 3.53, 3.11, 2.99 and 2.68 eV for Mg2RuH6, Ca2RuH6, Sr2RuH6 and Ba2RuH6, respectively. Calculated density of states spectra demonstrates that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. Optical spectra in a wide energy range from 0 to 30 eV have been provided and the origin of the observed peaks and structures has been assigned. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time. Voir les détails
Mots clés : Ruthenium-based hydrides; first-principles calculations; elastic constants; optical properties; electronic
Microstructure and Magnetic Properties of NiP Alloys
Ni-P alloys were prepared by electrodeposition on a copper substrate at different plating conditions (applied potential and deposition time). The morphology, composition, microstructure, structure, and magnetic properties of the films were investigated by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and vibrating sample magnetometry, respectively. The phosphorous content is about 8.6–12.2 at.%. The deposits exhibit either a nanocomposite structure where Ni(P)–1 and Ni(P)–2 solid solutions are embedded into an amorphous matrix, or a mixture of Ni2P phosphide and Ni(P)–1 and Ni(P)–2 solid solutions. The coercivity and magnetization are plating condition dependent. All samples exhibit a soft magnetic character with coercivity lower than 58 Oe. The squareness ratio Mr/Ms values that are in the range 0.019–0.123 correspond to a multidomain (<0.1) for all samples except sample B (−1.15 V, 10 min) which falls into a pseudo-single domain (Mr/Ms = 0.123). Voir les détails
Mots clés : Electrodeposition Ni-P alloys Microstructure Magnetic properties X-ray diffraction
Physical investigations on perovskite LaMnO3-δ sprayed thin films for spintronic applications
Oxygen deficient LaMnO3 thin films were successfully grown on glass substrate by spray pyrolysis at 460 °C. XRD studies show oxygen vacancies corresponding to the orthorhombic La4Mn4O11 with (040) preferential orientation. Optical properties were investigated through optical band gap and Urbach energy. The dispersion of the refractive index was discussed in terms of both Cauchy and Wemple & Di-domenico models. Raman spectroscopy shows the band positions corresponding to LaMnO3 with a shift related to oxygen deficiency. Electrical properties were quantified using impedance spectroscopy technique within frequency range of 5 Hz–13 MHz at various temperatures. Both the DC conductivity and relaxation frequency were thermally activated with activation energy around 0.9 eV. Also, AC conductivity was investigated through Jonscher law. Finally, magnetic measurements at room temperature using vibrating sample magnetometer (VSM) technique show ferromagnetic behavior of these ternary sprayed thin films. Voir les détails
Mots clés : Thin films, Magnetic Properties, Raman spectroscopy, Impedance spectroscopy, X-ray diffraction, Dielectric properties
Oi and Cs Impurities Study on the Edge of Si-mc Ingot for Photovoltaic Applications
The objective of this work is determining the substitutional carbon ([Cs]) and interstitial oxygen ([Oi]) concentrations in the edge of the multicrystalline silicon ingot (mc-Si) for photovoltaic applications obtained by the heat exchanger method (HEM). Some calculations of [Cs] and [Oi] was obtain by the Fourier Transform InfraRed spectroscopy (FTIR). The results obtained for [Cs] give an increase of bottom-up of the ingot: 130 ppm to 150 ppm. The results obtained for the [Oi] give constant concentrations throughout the edge of the ingot with an author of concentration 325 ppm. Voir les détails
Mots clés : Crystallization, mc-Si, HEM, FTIR, [Cs], [Oi]